Mail sorting equipment is in widespread use today. Automated location and detection of addresses on standard envelopes at high throughput rates has long been mastered. In the field of large-format envelopes and parcels (e.g. DIN A4, B4) too there has recently been a development with regard to automated address detection (cf. DE-C-195 32 842).
However, the proportion of such mail being sent vacuum sealed in plastic sheet is steadily increasing. Consequently, the detection of mail enclosed entirely in plastic sheeting or of mail with plastic strip areas--such as a plastic-sheeted window in a standard paper envelope or a label mounted on a plastic strip--is becoming more and more important.
Precise detection of plastic strips and/or areas of plastic is important for the following reasons:
The result of the read operation is often imprinted on the envelope as a barcode. Such barcodes cannot be affixed directly to the plastic, however, as there is a risk of their being blurred. A special label must therefore be affixed to the mail, resulting in additional cost which is avoidable on paper envelopes.
On the other hand, if a label of the said kind and its position on a plastic covering can be localized, the position of the recipient's address or barcode is thereby automatically identified.
The same applies where it is possible to detect a window and its position on a standard paper envelope.